1. Technical Field
The invention is related generally to can making machinery and more particularly to a transfer apparatus and method for translating or moving can blanks through a redraw press.
2. Background Information
Redraw presses generally include a die having a plurality of can receiving cavities which may sequentially have smaller diameters in the downstream direction. Pistons or punches which correspond to each of these cavities and/or may be aligned therewith in order to move into and out of the cavities to press a can blank within the cavity in order to sequentially transform the can blank into smaller and smaller diameters. A transfer mechanism is used to move the can blanks downstream into respective positions aligned with the respective cavities so that the can blanks are properly aligned for the punches to force the can blank into the corresponding cavity.
Various problems are known in the art which may be partly related to the type of metal or alloy used to make the can blanks or containers, the container strength, container height, container diameter and the speed with which the blanks or containers or cans move through the redraw press. For instance, the transfer mechanism must be set to grasp a container of a given diameter in order to properly carry or transfer it from one position to another. In addition, a change in the metal alloy or the thickness of the container wall changes the strength of the container such that a container of a given strength may need to be handled differently than another container of a different strength. For instance, a container of a lesser strength may need to be held more gingerly in order to prevent damage to the container. Such a container may also need to be held for a longer period of time just prior to downstroke of the punch in order to make sure that the container or blank is properly aligned so that the punch will not damage the blank or the canning machine. The desire within the industry to make containers or cans of a lighter and lighter weight naturally increases the difficulty with respect to handling containers having thinner walls and/or made from weaker alloys, such as aluminum alloys.
Some transfer mechanisms use magnets for steel containers in order to hold the containers in the proper location. However, the use of a magnet to help position a container in this manner will also hinder the next movement of the same container. Furthermore, magnets of course will not assist with the positioning of aluminum containers or other non-magnetic metals.
The transfer mechanism of redraw presses typically utilizes a pair of can gripping members which move inwardly toward one another and outwardly away from one another whereby their inward movement allows them to grasp or grip a can blank or container and their outward movement allows them to release the container. Thus, these gripping members will move inwardly in an axial direction to grasp a given can blank or container, and then move longitudinally downstream while continuing to grasp or hold the container in order to move the container to the next position or station for subsequent punching by a smaller diameter punch. The standard mechanical transfer mechanism utilizes various mechanical cams and linkages which are limited in various features. As will be readily understood, can manufacturers wish to produce their cans as quickly as possible, and thus have a tendency to increase the speed in which the stamping operation proceeds. However, the standard transfer mechanism cannot operate at certain higher speeds without causing expensive damage to the machinery, especially the die and piston or punch. More particularly, as the operational speed of the machine is increased, the standard transfer mechanism tends to throw a container or can blank generally into position in a sloppy manner as opposed to controlling it and holding it in the desired position. Due to the configuration of the standard transfer mechanism, the various moving parts thereof all move at interrelated ratios. As a result, when the operation reaches a certain speed, the gripping members either throw the can blank toward the desired position in an inaccurate manner or are unable to hold the blank in the desired position long enough to ensure that the blank is accurately placed prior to its being punched. The faster the operation, the longer the time period or duration that the can blank or container remains free of control or restraint. Thus, there is a need in the art to overcome these and various other problems.